The invention relates to a piezoelectric element with a multi-layer construction of piezoelectric layers, and a method for producing it, for example to produce a piezoelectric actuator that is used to actuate a mechanical component such as a valve or the like, according to the generically defined features of the main claim.
It is generally known that a piezoelectric element can be comprised of a material with a suitable crystalline structure in order to exploit the so-called piezoelectric effect. When an external electrical current is applied, the piezoelectric element reacts mechanically, which produces a pressure or tension in a predeterminable direction depending on the crystalline structure and the region to which the electrical current is applied. The piezoelectric actuator here can be made up of multiple layers (multi-layer actuators) in which the electrodes used to apply the electrical current are respectively disposed between the layers. The internal electrodes here are respectively offset by a certain amount in relation to the external electrodes so that no short circuit occurs there. Stacking the individual piezoelectric layers is very expensive because several hundred individual foil layers must be separately processed.
The piezoelectric element described at the beginning, with a multi-layer construction of piezoelectric layers, which have electrodes disposed between them that are contacted on alternating sides, can advantageously be a component of a piezoelectric actuator which is used to actuate a mechanical component such as a valve or the like. According to the invention, the individual piezoelectric layers are comprised of a continuous foil made of piezoceramic that can be folded during manufacturing and are provided entirely or partially with electrically conductive electrodes.
In a preferred embodiment, the foil is advantageously made to be flexible through the application of solvents and, except for a predetermined region at the ends in the longitudinal direction, is metallized on both sides, for example also by means of printing or sputtering, in order to produce the electrodes. In this connection, the predetermined regions without electrode material are provided at the end of the folded layers to avoid causing short circuits in the piezoelectric element after the attachment of external electrodes.
On the respective outside, in the bending region of the folded ceramic layer, the external electrodes can be easily attached to produce the alternating-side contact with the metallized layer; the external electrodes can be comprised of an electrically conductive screen or mesh, or can be comprised of a corrugated electrode.
In order to insulate the entire piezoelectric element in relation to the outside, the multi-layer construction of piezoelectric layers is provided with an electrically insulating ceramic plate at the end of the folded layers.
In an advantageous method for producing a piezoelectric element of the type described above, the following manufacturing steps are executed:
The piezoelectric foil is made flexible by the solvent and is cut to the width of the piezoelectric element.
The piezoelectric foil is metallized on both sides except for the predetermined end regions.
The piezoelectric foil is folded by being bent at predetermined intervals.
The folded packet is laminated.
The folded packet is sintered.
The external electrodes are attached to the metallized layer in the bending region by means of soldering.
Alternatively, before the sintering: An electrically insulating top and bottom plate made of piezoceramic are affixed to the outer piezoelectric layers.